Fluoridated hydroxyapatite coatings on titanium obtained by electrochemical deposition

Hydroxyapatite (HA) and fluoridated hydroxyapatite (FHA) coatings were deposited on titanium substrates using an electrochemical technique. Different concentrations of F− ions were incorporated into the apatite structure by adding NaF into the electrolyte. Typical apatite structures were obtained for all the coatings after electrodeposition and subsequent post-treatment, including alkaline immersion and vacuum calcination. The coatings were uniform and dense, with a thickness of ∼5 μm. When the F-concentration was higher than 0.012 M in the electrolyte, a saturation of F in the coating occurred and the F/Ca ratio in the coatings became almost constant (F/Ca ratio = 0.125). The FHA coatings showed higher bonding strength and lower dissolution rate than HA coating, particularly for those with a fluoridation level of 0.5–0.625. Compared with pure Ti, FHA and HA coatings exhibited higher biological affinity like cell proliferation and alkaline phosphatase activity. Regarding clinical application, it is suggested that a moderate content of F, such as Ca5(PO4)3(OH)0.375−0.5F0.5−0.625, be most suitable as a compromise among cell attachment, cell proliferation, apatite deposition and dissolution resistance.